Metanephrine

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Fasting Required

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Catecholamine metabolites.

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Metanephrine Test - Comprehensive Medical Information Guide

Why is it done?
- Measures the breakdown products of catecholamines (epinephrine and norepinephrine) to detect abnormal hormone production
- Primary indication: Screening for pheochromocytoma, a rare neuroendocrine tumor of the adrenal medulla that produces excessive catecholamines
- Evaluates patients with unexplained hypertension, particularly resistant hypertension or hypertension with palpitations and sweating episodes
- Assists in monitoring paragangliomas and detecting metastatic disease in patients with known pheochromocytoma
- Used in patients with genetic predisposition syndromes (MEN2A, MEN2B, Von Hippel-Lindau disease, Neurofibromatosis type 1)
- Typically performed when patients present with symptoms such as severe headaches, profuse sweating, palpitations, tremor, and paroxysmal hypertension
Normal Range
- Plasma Metanephrine: 0.0-0.90 nmol/L or 0-15 pg/mL (reference ranges may vary by laboratory)
- Plasma Normetanephrine: 0.0-1.20 nmol/L or 0-30 pg/mL (reference ranges may vary by laboratory)
- 24-hour Urine Metanephrine: 24-204 mcg/24 hours or 12-102 nmol/24 hours
- 24-hour Urine Normetanephrine: 35-400 mcg/24 hours or 18-202 nmol/24 hours
- Interpretation: Normal (Negative) results indicate no evidence of pheochromocytoma or paraganglioma; results typically fall within reference limits with metanephrine and normetanephrine at or below the upper limit of normal
- Elevated/Positive results indicate levels above the upper reference limit; values typically 4-10 times normal in pheochromocytoma cases, though mild elevations (1-4 times normal) may require repeat testing
- Borderline values (slightly above normal but <4x upper limit) warrant repeat testing and additional diagnostic imaging to rule out false positives
Interpretation
- Markedly Elevated Results (>4 times upper limit of normal): Strong indication of pheochromocytoma or paraganglioma; warrants immediate imaging studies (CT, MRI, or PET-CT) and endocrinology consultation; high diagnostic sensitivity and specificity for catecholamine-secreting tumors
- Mildly Elevated Results (1-4 times upper limit of normal): Suggestive but not diagnostic; repeat testing recommended as false positives are common; patient preparation and medication review are critical
- Normal Results: Pheochromocytoma is unlikely if testing conditions were optimal; does not completely exclude diagnosis in symptomatic patients or those with genetic predisposition
- Selective Elevation (elevated normetanephrine or metanephrine only): May indicate location of tumor (extra-adrenal paragangliomas more commonly produce normetanephrine)
- Factors affecting interpretation: Medications (decongestants, sympathomimetics, tricyclic antidepressants, stimulants can elevate results); physical or emotional stress; sleep deprivation; caffeine intake; inadequate fasting or improper patient positioning before blood draw
- Clinical significance: Test has excellent negative predictive value (>95%), making it ideal for ruling out pheochromocytoma in most patients; positive results require confirmation with imaging and biochemical clonidine suppression test if borderline
Associated Organs
- Primary organ system: Adrenal medulla and sympathetic nervous system; test directly measures metabolic byproducts of catecholamines produced by neuroendocrine tissue
- Pheochromocytoma: Catecholamine-secreting tumor arising from chromaffin cells of adrenal medulla in ~90% of cases; ~10% are extra-adrenal paragangliomas
- Paragangliomas: Extra-adrenal neuroendocrine tumors in sympathetic chain; may occur in chest, abdomen, neck, or bladder; often associated with genetic syndromes
- Associated conditions: Hypertension (secondary hypertension due to excessive catecholamine production); cardiovascular complications including myocardial infarction, arrhythmias, congestive heart failure, and sudden cardiac death from catecholamine surges
- Metabolic effects: Hyperglycemia, weight loss, and metabolic acidosis from excessive catecholamine effects on glucose and lipid metabolism
- Genetic syndromes associated: Multiple Endocrine Neoplasia type 2A and 2B (MEN2), Von Hippel-Lindau disease, Neurofibromatosis type 1 (NF1), familial paraganglioma syndrome
- Potential complications if untreated: Hypertensive crisis with end-organ damage, stroke, myocardial infarction, acute coronary syndrome, cardiomyopathy, pulmonary edema, and malignant hypertension
Follow-up Tests
- Confirmatory testing: Clonidine suppression test (useful for borderline results to distinguish true pheochromocytoma from false positives); plasma free catecholamines may be ordered for additional confirmation
- Imaging studies: CT chest/abdomen/pelvis or MRI for localization of adrenal or extra-adrenal tumors; functional imaging with MIBG scan (123I-metaiodobenzylguanidine) or PET scan for detection of metastatic disease or extra-adrenal paragangliomas
- Repeat metanephrine testing: If initial result is borderline (mildly elevated), repeat testing after 1-2 weeks and optimization of patient preparation factors; ensures accuracy before proceeding with expensive imaging
- Genetic testing: If pheochromocytoma/paraganglioma confirmed, genetic testing for SDHA, SDHB, SDHD, VHL, RET, and NF1 mutations to identify hereditary predisposition and guide family screening
- Blood pressure monitoring: Baseline and ongoing assessment given increased cardiovascular risk; electrocardiogram if indicated for arrhythmia evaluation
- Post-operative monitoring: Serial metanephrine levels after surgical resection to confirm tumor removal and detect recurrence; baseline measurement needed before surgery for comparison
- Long-term surveillance: Annual or biennial metanephrine testing in patients with genetic syndromes predisposing to pheochromocytoma (MEN2, VHL, NF1)
- Plasma free catecholamines: Alternative or complementary test; provides direct measurement of epinephrine and norepinephrine rather than metabolites
Fasting Required?
- Fasting: No strict fasting required for plasma metanephrine testing; however, certain dietary and lifestyle modifications are recommended for optimal test accuracy
- Patient preparation (Critical for accurate results): Avoid caffeine for 24-48 hours before test (found in coffee, tea, chocolate, colas, energy drinks); caffeine increases catecholamine levels and causes false positives
- Medication review and timing: Discontinue or adjust medications that interfere with metanephrine levels for 5-7 days before testing if possible (requires physician approval); key offenders include decongestants (pseudoephedrine, phenylephrine), sympathomimetics, tricyclic antidepressants (amitriptyline, imipramine), stimulants (methylphenidate, amphetamines), and some antipsychotics
- Physical positioning and stress: Remain seated quietly for 5-10 minutes before blood draw to avoid falsely elevated results from exertion; blood draw should be performed while patient is supine or sitting after resting period
- Avoid during acute illness: Do not perform testing during acute stress, severe infection, acute illness, or within 2-3 weeks after myocardial infarction (transient elevation of metanephrines occurs)
- Dietary modifications: Continue normal diet but avoid foods with high tyramine content (aged cheeses, cured meats, soy products, fermented foods) for 24 hours prior; avoid foods high in catecholamines
- 24-hour urine collection: Instructions provided by laboratory; typically requires collection in specialized containers; patient should maintain normal diet and activity during collection period

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